Temperature sensor

ABSTRACT

A temperature sensor generates a variable voltage whose level decreases linearly as a temperature increases, and compares the variable voltage with first and second reference voltages to generate first and second temperature codes to measure the temperature.

CROSS-REFERENCES TO RELATED APPLICATIONS

The present application claims priority under 35 U.S.C 119(a) to Koreanapplication number 10-2010-0017327, filed on Feb. 25, 2010, in theKorean intellectual property Office, which is incorporated herein byreference in its entirety set forth in full.

BACKGROUND

To meet the demands of the high performance of electronic systems suchas personal computers or electronic communication devices, nonvolatilesemiconductor memory devices such as DRAMs mounted as memory deviceshave been designed to operate at higher speed and have become highlyintegrated. Since semiconductor memory devices mounted on battery-drivensystems such as mobile phones or notebook computers desperately requirea low power consumption characteristic, many efforts and developmentshave been made to reduce an operating current and a standby current.

A data retention characteristic of a DRAM cell consisting of onetransistor and one storage capacitor is very sensitive to temperature.Therefore, it may be necessary to adjust the operating conditions ofcircuit blocks inside semiconductor integrated circuits, depending onthe variation in an ambient temperature. For example, DRAMs used inmobile products adjust a refresh period, depending on the variation inan ambient temperature.

Temperature sensors, such as a Digital Temperature Sensor Regulator(DTSR), an Analog Temp Sensor Regulator (ATSR), and a DigitalTemperature Compensated Self Refresh (DTCSR), are used to adjust theoperating conditions depending on the variation in the ambienttemperature.

A DTCSR is a temperature sensor which is used to sense an ambienttemperature and determine a refresh period of memory cells. A typicalDTCSR senses an ambient temperature to generate a variable voltage, andcompares the level of the variable voltage with the level of a referencevoltage to generate a code signal. In the DTCSR, the variable voltage isgenerated from a circuit which is implemented with an NMOS transistor, aPMOS transistor, a resistor, and so on. Therefore, the variable voltagechanges nonlinearly with the temperature variation, and it is difficultto predict the voltage variation which is caused by the processvariation. Furthermore, it is difficult to measure the temperatureexactly because the voltage variation has a gentle slope with respect tothe temperature voltage.

SUMMARY

An embodiment of the present invention relates to a temperature sensorwhich is capable of measuring a temperature exactly to thereby maintaina normal operation of a semiconductor memory device.

In one embodiment, a temperature sensor includes: a reference voltagegeneration unit configured to divide a driving voltage and generate areference voltage; a first resistor coupled between a driving voltageterminal and a first node through which a nonlinear voltage isoutputted; a first switch coupled between the first node and a groundvoltage terminal, and configured to be turned on in response to thereference voltage; a second resistor coupled between the driving voltageterminal and a second node through which a variable voltage isoutputted; a second switch coupled between the second node and a thirdnode, and configured to be turned on in response to the nonlinearvoltage; a third resistor coupled between the third node and the groundvoltage terminal; and a temperature code generation unit configured tocompare the level of the reference voltage with the level of thevariable voltage, and generate a temperature code.

In another embodiment, a temperature sensor includes: a referencevoltage generation unit configured to divide a driving voltage andgenerate a reference voltage; a variable voltage generation unitconfigured to generate a nonlinear voltage in response to the referencevoltage and a bias resistor, whose resistance is set in response to atest mode signal or a fuse cutting, and generates a variable voltagefrom the nonlinear voltage; and a temperature code generation unitconfigured to compare the level of the reference voltage with the levelof the variable voltage, and generate a temperature code.

In another embodiment, a temperature sensor includes: a referencevoltage generation unit configured to divide a driving voltage andgenerate first and second reference voltages; a variable voltagegeneration unit configured to generate a variable voltage in response tothe first reference voltage and a bias resistor; a first temperaturecode generation unit configured to compare the level of the firstreference voltage with the level of the variable voltage, and generate afirst temperature code; and a second temperature code generation unitconfigured to compare the level of the second reference voltage with thelevel of the variable voltage, and generate a second temperature code.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features and other advantages will be moreclearly understood from the following detailed description taken inconjunction with the accompanying drawings, in which:

FIG. 1 is a block diagram illustrating the configuration of atemperature sensor according to an embodiment of the present invention;

FIG. 2 is a circuit diagram illustrating the configuration of areference voltage generation unit included in the temperature sensor ofFIG. 1;

FIG. 3 is a circuit diagram illustrating the configuration of a variablevoltage generation unit included in the temperature sensor of FIG. 1according to an embodiment of the present invention;

FIG. 4 is a graph explaining the operation of the variable voltagegeneration unit of FIG. 3;

FIG. 5 is a configuration diagram of a variable voltage generation unitincluded in the temperature sensor of FIG. 1 according to anotherembodiment of the present invention;

FIG. 6 is a circuit diagram illustrating the configuration of a decodingsignal generator included in the variable voltage generation unit ofFIG. 5;

FIG. 7 is a circuit diagram illustrating the configuration of a biasresistor controller included in the variable voltage generation unit ofFIG. 5;

FIG. 8 is a block diagram illustrating the configuration of atemperature sensor according to another embodiment of the presentinvention; and

FIG. 9 is a block diagram illustrating the configuration of a referencevoltage generation unit included in the temperature sensor of FIG. 8.

DESCRIPTION OF SPECIFIC EMBODIMENTS

Hereinafter, embodiments of the present invention will be described withreference to accompanying drawings. However, the embodiments are forillustrative purposes only and are not intended to limit the scope ofthe invention.

FIG. 1 is a block diagram illustrating the configuration of atemperature sensor according to an embodiment of the present invention.

Referring to FIG. 1, the temperature sensor includes a reference voltagegeneration unit 1, a variable voltage generation unit 2, and atemperature code generation unit 3. The reference voltage generationunit 1 is operatively coupled to the variable voltage generation unit 2,and to the temperature code generation unit 3. The variable voltagegeneration unit 2 is operatively coupled to the temperature codegeneration unit 3. The terminology “operatively coupled” as used hereinrefers to coupling that enables operational and/or functionalcommunication and relationships therebetween and may include anyintervening items necessary to enable such communication such as, forexample, data communication buses or any other necessary interveningitems that one of ordinary skill would understand to be present. Also,it is to be understood that other intervening items may be presentbetween “operatively coupled” items even though such other interveningitems are not necessary to the functional communication facilitated bythe operative coupling. For example, a data communication bus mayprovide data to several items along a pathway along which two or moreitems are operatively coupled, etc. Such operative coupling is showngenerally in the figures described herein.

FIG. 2 illustrates an embodiment in which the reference voltagegeneration unit 1 includes resistors R11 and R12 coupled between adriving voltage (VDRV) terminal and a ground voltage (VSS) terminal, andconfigured to divide a driving voltage VDRV and generate a referencevoltage VREF whose level corresponds to a specific temperature.

As illustrated in FIG. 3, the variable voltage generation unit 2according to an embodiment of the present invention includes a firstnonlinear voltage generation section 20 and a first linear voltagegeneration section 21. The first nonlinear voltage generation section 20is operatively coupled to the first linear voltage generation section 21and includes a resistor R20 and an NMOS transistor N20. Specifically,the resistor R20 is coupled between the driving voltage (VDRV) terminaland a node nd20, through which a first nonlinear voltage VN1 isoutputted. The NMOS transistor N20 is coupled between the node nd20 andthe ground voltage (VSS) terminal, and configured to operate as a switchwhich is turned on in response to the reference voltage VREF. The NMOStransistor N20 is designed so that a smaller amount of turn-on currentflows as the temperature increases. The first linear voltage generationsection 21 includes a resistor R21, an NMOS transistor N21, and aresistor R22. Specifically, the resistor R21 is coupled between thedriving voltage (VDRV) terminal and a node nd21, through which avariable voltage VTEMP is outputted. The NMOS transistor N21 is coupledbetween the node nd21 and a node nd22, and configured to operate as aswitch which is turned on in response to the first nonlinear voltageVN1. The resistor R22 is coupled between the node nd22 and the groundvoltage (VSS) terminal. The NMOS transistor N21 is designed so that alarger amount of turn-on current flows as the temperature increases.

The operation of the variable voltage generation unit 2 of FIG. 3 willbe described below with reference to FIG. 4.

As illustrated in FIG. 4, the first nonlinear voltage generation section20 receives the reference voltage VREF and generates the first nonlinearvoltage VN1 the level of which increases nonlinearly as the temperatureincreases. The reason why the first nonlinear voltage VN1 generated fromthe first nonlinear voltage generation section 20 has the nonlinearcharacteristic is that a level rise slope according to the temperatureincrease of the first nonlinear voltage VN1 is reduced by the NMOStransistor N20 designed so that a smaller amount of the turn-on currentflows as the temperature increases.

Thereafter, the first linear voltage generation section 21 receives thefirst nonlinear voltage VN1 and generates the variable voltage VTEMP. Asdescribed above, the temperature characteristic of the NMOS transistorN21 included in the first linear voltage generation section 21 isopposite to that of the NMOS transistor N20. Also, as the temperatureincreases, the level of the variable voltage VTEMP is linearly decreasedby the nonlinear characteristic of the first nonlinear voltage VN1.

As illustrated in FIG. 5, a variable voltage generation unit 2 accordingto another embodiment includes a second nonlinear voltage generationsection 22 and a second linear voltage generation section 25.

The second nonlinear voltage generation section 22 includes a decodingsignal generator 23, a bias resistor controller 24, which is operativelycoupled to the decoding signal generator 23, and an NMOS transistor N22which is operatively coupled to the bias resistor controller 24. TheNMOS transistor N22 is coupled between a node nd23 and a ground voltage(VSS) terminal, and configured to operate as a switch which is turned onin response to a reference voltage VREF. The NMOS transistor N22 isdesigned so that a smaller amount of turn-on current flows as thetemperature increases.

As illustrated in FIG. 6, the decoding signal generator 23 includes afuse signal generation circuit 230 and a selective output circuit 231.

The fuse signal generator 230 is operatively coupled to the selectiveoutput circuit 231, and includes a PMOS transistor P20, a first fuseF20, and a second fuse F21. The PMOS transistor P20 is coupled between apower supply voltage (VDD) terminal and a node nd200, and configured toreceive an inversion signal of a power-up signal PWRUP, at the P20 gateterminal, through an inverter IV20 and thereby pull up the node nd200.The first fuse F20 is coupled between the node nd200 and a node nd201,and the second fuse F21 is coupled between the node nd200 and a nodend202. The fuse signal generator 230 configured as above is suppliedwith a power supply voltage VDD in response to the power-up signalPWRUP, which changes to a high level after the completion of a power-upduration, and generates a first fuse signal FUSE1 and a second fusesignal FUSE2. “High level” and “low level” refers to, for example,voltage levels and/or voltage ranges that are predetermined to representthe high level or low level and not necessarily any specific values. Itis to be understood that “high level” and “low level” may also bereferred to as “logic levels” for example, a “high logic level” and a“low logic level,” respectively. Such “logic levels” may also beunderstood to correspond to logical or binary bit values, for example,where a “low logic level” corresponds to a logical “0” and a “high logiclevel” corresponds to a logical “1” or vice versa depending on specificimplementations in the various embodiments. The levels of the first fusesignal FUSE1 and the second fuse signal FUSE2 are determined accordingto whether the first fuse F20 and the second fuse F21 are cut or not.That is, when the first fuse F20 is not cut, the first fuse signal FUSE1having a high level is generated. When the first fuse F20 is cut, thefirst fuse signal FUSE1 having a low level is generated. Also, when thesecond fuse F21 is not cut, the second fuse signal FUSE2 having a highlevel is generated. When the second fuse F21 is cut, the second fusesignal FUSE2 having a low level is generated.

The selective output circuit 231 includes a first transfer gate T20, asecond transfer gate T21, a third transfer gate T22, and a fourthtransfer gate T23. The first transfer gate T20 is configured to transferthe first fuse signal FUSE1 as a first decoding signal DEC1 in responseto a test enable signal TMEN and an inverted test enable signal TMENB.The second transfer gate T21 is configured to transfer a first test modesignal TM1 as the first decoding signal DEC1 in response to the testenable signal TMEN and the inverted test enable signal TMENB. The thirdtransfer gate T22 is configured to transfer the second fuse signal FUSE2as a second decoding signal DEC2 in response to the test enable signalTMEN and the inverted test enable signal TMENB. The fourth transfer gateT23 is configured to transfer a second test mode signal TM2 as thesecond decoding signal DEC2 in response to the test enable signal TMENand the inverted test enable signal TMENB. When the test enable signalTMEN is at a high level, the selective output circuit 231 configured asabove transfers the first test mode signal TM1 as the first decodingsignal DEC1, and transfers the second test mode signal TM2 as the seconddecoding signal DEC2. Also, when the test enable signal TMEN is at a lowlevel, the selective output circuit 231 transfers the first fuse signalFUSE1 as the first decoding signal DEC1, and transfers the second fusesignal FUSE2 as the second decoding signal DEC2. The first test modesignal TM1 and the second test mode signal TM2 may be generatedinternally or applied from the outside.

As illustrated in FIG. 7, the bias resistor controller 24 may include aresistor R240, a resistor R241, an NMOS transistor N200, a resistorR242, and an NMOS transistor N201. The resistor R240 is coupled betweenthe driving voltage (VDRV) terminal and a node nd240, and the resistorR241 is coupled between the node nd240 and a node nd241. The NMOStransistor N200 is coupled in parallel to the resistor R241 between thenode nd240 and the node nd241, and configured to be turned on inresponse to the first decoding signal DEC1 received at the N200 gateterminal. The resistor R242 is coupled between the node nd241 and thenode nd23. The NMOS transistor N201 is coupled in parallel to theresistor R242 between the node nd241 and the node nd23. The NMOStransistor N201 is configured to be turned on in response to the seconddecoding signal DEC2 received at the N201 gate terminal.

The second linear voltage generation section 25, which is operativelycoupled to the second nonlinear voltage generation section 22, mayinclude a resistor R23, an NMOS transistor N23, and a resistor R24. Theresistor R23 is coupled between the driving voltage (VDRV) terminal anda node nd24, through which the variable voltage VTEMP is outputted. TheNMOS transistor N23 is coupled between the node nd24 and a node nd25,and configured to operate as a switch which is turned on in response tothe second nonlinear voltage VN2 at the N23 gate terminal. The resistorR24 is coupled between the node nd25 and the ground voltage (VSS)terminal. The NMOS transistor N23 is designed so that a larger amount ofturn-on current flows as the temperature increases.

As described above, the variable voltage generation unit 2 of FIG. 5 canadjust the bias resistance between the driving voltage (VDRV) terminaland the node nd23 according to the first and second test mode signalsTM1 and TM2 or according to whether the first fuse F20 and the secondfuse F21 are cut or not.

The temperature code generation unit 3 may be implemented with adifferential amplifier circuit which compares the level of the referencevoltage VREF with the level of the variable voltage VTEMP and generatesa temperature code TQ_CODE. The temperature code TQ_CODE is enabled whenthe level of the variable temperature VTEMP is lower than the level ofthe reference voltage VREF, and disabled when the level of the variablevoltage VTEMP is higher than the level of the reference voltage VREF.The level of the variable voltage VTEMP decreases linearly as thetemperature increases. In other words, the temperature code generationunit 3 generates the temperature code TQ_CODE when the variable voltageVTEMP is lower than the reference voltage VREF. Therefore, the case inwhich the variable voltage VTEMP is generated to be lower than thereference voltage VREF means that the temperature is higher than aspecific temperature corresponding to the level of the reference voltageVREF.

In summary, in the temperature sensor according to an embodiment of thepresent invention, the variable voltage generation unit 2 implementedwith the resistors and the NMOS transistors generates the variablevoltage VTEMP whose level decreases linearly as the temperatureincreases, and the level of the variable voltage VTEMP is compared withthe level of the reference voltage VREF to generate the temperature codeTQ_CODE. The level of the variable voltage VTEMP generated from thetemperature sensor according to the embodiment of the present inventiondecreases linearly as the temperature increases, and it is easy topredict the voltage variation according to the process variation.Furthermore, the temperature can be exactly measured.

FIG. 8 is a block diagram illustrating the configuration of atemperature sensor according to another embodiment of the presentinvention.

Referring to FIG. 8, the temperature sensor according to anotherembodiment of the present invention includes a reference voltagegeneration unit 4, a variable voltage generation unit 5, a firsttemperature code generation unit 6, and a second temperature codegeneration unit 7. The reference voltage generation unit 4 isoperatively coupled to the first temperature code generation unit 6, thevariable voltage generation unit 5 and the second temperature codegeneration unit 7. The variable voltage generation unit 5 outputs VTEMP,and is operatively coupled to both the first temperature code generationunit 6 and the second temperature code generation unit 7.

As illustrated in FIG. 9, the reference voltage generation unit 4 mayinclude resistors R40, R41 and R42 coupled between a driving voltage(VDRV) terminal and a ground voltage (VSS) terminal, and configured todivide a driving voltage VDRV to generate a first reference voltageVREF1 and a second reference voltage VREF2. The first reference voltageVREF1 and the second reference voltage VREF2 have levels correspondingto a specific temperature.

The variable voltage generation unit 5 is configured to receive thefirst reference voltage VREF1 to generate a variable voltage VTEMP whoselevel decreases linearly as the temperature increases. The variablevoltage generation unit 5 can be implemented with the circuits whichhave been described above with reference to FIGS. 3 to 8.

The first temperature code generation unit 6 may be implemented with adifferential amplifier circuit which compares the level of the firstreference voltage VREF1 with the level of the variable voltage VTEMP andgenerates a first temperature code TQ_CODE1. The first temperature codeTQ_CODE1 is enabled when the level of the variable voltage VTEMP islower than the level of the first reference voltage VREF1, and disabledwhen the level of the variable voltage VTEMP is higher than the level ofthe first reference voltage VREF1.

The second temperature code generation unit 7 may be implemented with adifferential amplifier circuit which compares the level of the secondreference voltage VREF2 with the level of the variable voltage VTEMP andgenerates a second temperature code TQ_CODE2. The second temperaturecode TQ_CODE2 is enabled when the level of the variable voltage VTEMP islower than the level of the second reference voltage VREF2, and disabledwhen the level of the variable voltage VTEMP is higher than the level ofthe second reference voltage VREF2.

In summary, the temperature sensor according to the embodiment of thepresent invention generates the variable voltage VTEMP whose leveldecreases linearly as the temperature increases, and compares the levelof the variable voltage VTEMP with the levels of the first and secondreference voltages VREF1 and VREF2 to generate the first and secondtemperature codes TQ_CODE1 and TQ_CODE2. Therefore, the temperaturesensors according to the embodiments of the present invention canmeasure the temperature more precisely.

The embodiments of the present invention have been disclosed above forillustrative purposes. Those skilled in the art will appreciate thatvarious modifications, additions and substitutions are possible, withoutdeparting from the scope and spirit of the invention as disclosed in theaccompanying claims.

1. A temperature sensor comprising: a reference voltage generation unitconfigured to divide a driving voltage and generate a reference voltage;a first resistor coupled between a driving voltage terminal and a firstnode through which a nonlinear voltage is outputted; a first switchcoupled between the first node and a ground voltage terminal, andconfigured to be turned on in response to the reference voltage; asecond resistor coupled between the driving voltage terminal and asecond node through which a variable voltage is outputted; a secondswitch coupled between the second node and a third node, and configuredto be turned on in response to the nonlinear voltage; a third resistorcoupled between the third node and the ground voltage terminal; and atemperature code generation unit configured to compare the referencevoltage with the variable voltage, and generate a temperature code. 2.The temperature sensor of claim 1, wherein the nonlinear voltageincreases nonlinearly, depending on a temperature variation.
 3. Thetemperature sensor of claim 2, wherein the variable voltage decreaseslinearly, depending on the temperature variation.
 4. The temperaturesensor of claim 3, wherein the first switch comprises an NMOS transistorconfigured so that a smaller amount of turn-on current flows astemperature increases, and the second switch comprises an NMOStransistor configured so that a larger amount of turn-on current flowsas temperature increases.
 5. The temperature sensor of claim 1, whereinthe temperature code generation unit is configured to generate thetemperature code when the variable voltage is lower than the referencevoltage.
 6. A temperature sensor comprising: a reference voltagegeneration unit configured to divide a driving voltage and generate areference voltage; a variable voltage generation unit, operativelycoupled to the reference voltage generation unit, configured to generatea nonlinear voltage in response to the reference voltage and a biasresistor, whose resistance is set in response to a test mode signal or afuse cutting, and generates a variable voltage from the nonlinearvoltage; and a temperature code generation unit, operatively coupled tothe reference voltage generation unit and the variable voltagegeneration unit, configured to compare the reference voltage with thevariable voltage, and generate a temperature code.
 7. The temperaturesensor of claim 6, wherein the variable voltage generation unitcomprises: a decoding signal generator configured to selectively outputa fuse signal or a test mode signal as a decoding signal in response toa test enable signal, the fuse signal being generated by the fusecutting; a bias resistor controller, operatively coupled to the decodingsignal generator, configured to control a bias resistance between adriving voltage terminal and an output node, through which the nonlinearvoltage is outputted, in response to the decoding signal; and a firstswitch coupled between the output node and a ground voltage terminal,and configured to be turned on in response to the reference voltage. 8.The temperature sensor of claim 7, wherein the decoding signalgeneration section comprises: a fuse signal generation circuitconfigured to generate first and second fuse signals in response tofirst or second fuses being cut, respectively; and a selective outputcircuit, operatively coupled to the fuse signal generation circuit,configured to selectively output the first fuse signal or a first testmode signal as a first decoding signal in response to the test enablesignal, and selectively output the second fuse signal or a second testmode signal as a second decoding signal in response to the test enablesignal.
 9. The temperature sensor of claim 8 wherein the fuse signalgeneration circuit comprises: a pull-up element coupled between a powersupply voltage terminal and a first node, and configured to pull up thefirst node in response to a power-up signal; a first fuse coupledbetween the first node and a second node; and a second fuse coupledbetween the first node and a third node.
 10. The temperature sensor ofclaim 8, wherein the selective output circuit comprises: a firsttransfer gate, operatively coupled to the fuse signal generationcircuit, configured to transfer the first fuse signal as the firstdecoding signal in response to the test enable signal; a second transfergate configured to transfer the first test mode signal as the firstdecoding signal in response to the test enable signal; a third transfergate, operatively coupled to the fuse signal generation circuit,configured to transfer the second fuse signal as the second decodingsignal in response to the test enable signal; and a fourth transfer gateconfigured to transfer the second test mode signal as the seconddecoding signal in response to the test enable signal.
 11. Thetemperature sensor of claim 7, wherein the bias resistor controllercomprises first and second resistors coupled in series between thedriving voltage terminal and the output node, and both terminals of atleast one of the first and second resistors are shorted together inresponse to the decoding signal.
 12. The temperature sensor of claim 7,wherein the variable voltage generation unit further comprises: a firstresistor coupled between the driving voltage terminal and a first nodethrough which the variable voltage is outputted; a second switch coupledbetween the first node and a second node, and configured to be turned onin response to the nonlinear voltage; and a second resistor coupledbetween the second node and a ground voltage.
 13. The temperature sensorof claim 6, wherein the temperature code generation unit generates thetemperature code when the variable voltage is lower than the referencevoltage.
 14. A temperature sensor comprising: a reference voltagegeneration unit configured to divide a driving voltage and generatefirst and second reference voltages; a variable voltage generation unit,operatively coupled to the reference voltage generation unit, configuredto generate a variable voltage in response to the first referencevoltage and a bias resistor; a first temperature code generation unit,operatively coupled to the reference voltage generation unit and thevariable voltage generation unit, configured to compare the firstreference voltage with the variable voltage, and generate a firsttemperature code; and a second temperature code generation unit,operatively coupled to the reference voltage generation unit and thevariable voltage generation unit, configured to compare the secondreference voltage with the variable voltage, and generate a secondtemperature code.
 15. The temperature sensor of claim 14, wherein thevariable voltage generation unit comprises: a first resistor coupledbetween a driving voltage terminal and a first node through which anonlinear voltage is outputted; a first switch coupled between the firstnode and a ground voltage terminal, and configured to be turned on inresponse to the first reference voltage; a second resistor coupledbetween the driving voltage terminal and a second node through which thevariable voltage is outputted; a second switch coupled between thesecond node and a third node, and configured to be turned on in responseto the nonlinear voltage; and a third resistor coupled between the thirdnode and the ground voltage terminal.
 16. The temperature sensor ofclaim 15, wherein the nonlinear voltage increases nonlinearly, dependingon a temperature variation.
 17. The temperature sensor of claim 16,wherein the variable voltage decreases linearly, depending on thetemperature variation.
 18. The temperature sensor of claim 17, whereinthe first switch comprises an NMOS transistor configured so that asmaller amount of turn-on current flows as temperature increases, andthe second switch comprises an NMOS transistor configured so that alarger amount of turn-on current flows as temperature increases.
 19. Thetemperature sensor of claim 14, wherein the variable voltage generationunit comprises: a decoding signal generator configured to selectivelyoutput a fuse signal or a test mode signal as a decoding signal inresponse to a test enable signal, the fuse signal being in response to afuse cutting; a bias resistor controller, operatively coupled to thedecoding signal generator, configured to control a bias resistancebetween a driving voltage terminal and an output node, through which anonlinear voltage is outputted, in response to the decoding signal; anda first switch coupled between the output node and a ground voltageterminal, and configured to be turned on in response to the firstreference voltage.
 20. The temperature sensor of claim 19, wherein thedecoding signal generator comprises: a fuse signal generation circuitconfigured to generate first and second fuse signals in response tofirst or second fuses being cut, respectively; and a selective outputcircuit, operatively coupled to the fuse signal generation circuit,configured to selectively output the first fuse signal or a first testmode signal as a first decoding signal in response to the test enablesignal, and selectively output the second fuse signal or a second testmode signal as a second decoding signal in response to the test enablesignal.
 21. The temperature sensor of claim 20 wherein the fuse signalgeneration circuit comprises: a pull-up element coupled between a powersupply voltage terminal and a first node, and configured to pull up thefirst node in response to a power-up signal; a first fuse coupledbetween the first node and a second node; and a second fuse coupledbetween the first node and a third node.
 22. The temperature sensor ofclaim 20, wherein the selective output circuit comprises: a firsttransfer gate, operatively coupled to the fuse signal generationcircuit, configured to transfer the first fuse signal as the firstdecoding signal in response to the test enable signal; a second transfergate configured to transfer the first test mode signal as the firstdecoding signal in response to the test enable signal; a third transfergate, operatively coupled to the fuse signal generation circuit,configured to transfer the second fuse signal as the second decodingsignal in response to the test enable signal; and a fourth transfer gateconfigured to transfer the second test mode signal as the seconddecoding signal in response to the test enable signal.
 23. Thetemperature sensor of claim 19, wherein the bias resistor controllercomprises first and second resistors coupled in series between thedriving voltage terminal and the output node, and both terminals of atleast one of the first and second resistors are shorted together inresponse to the decoding signal.
 24. The temperature sensor of claim 19,wherein the variable voltage generation unit further comprises: a firstresistor coupled between the driving voltage terminal and a first nodethrough which the variable voltage is outputted; a second switch coupledbetween the first node and a second node, and configured to be turned onin response to the nonlinear voltage; and a second resistor coupledbetween the second node and a ground voltage.
 25. The temperature sensorof claim 14, wherein the first temperature code generation unit isfurther configured to generate the first temperature code when thevariable voltage is lower than the first reference voltage, and thesecond temperature code generation unit is further configured togenerate the second temperature code when the variable voltage is lowerthan the second reference voltage.
 26. A temperature sensor comprising:a variable voltage generation unit, configured to generate a variablevoltage in response to a first reference voltage; a first temperaturecode generation unit, operatively coupled to the variable voltagegeneration unit, configured to compare the first reference voltage withthe variable voltage, and generate a first temperature code; and asecond temperature code generation unit, operatively coupled to thevariable voltage generation unit, configured to compare a secondreference voltage with the variable voltage, and generate a secondtemperature code.